Piston ring



June 17 1924.

B. D. COLEMAN ET AL PISTON RING Filed Sept. 29. 1920 Patented June 17, 1924.

vS'IATEE EAWJW BERTRAM DAWSO'N' COLEMAN AND JOHN S. BARNER, OF I HILADELPHIA, PENN- SYLVANIA.

PISTON RING.

Application filed September 29, 1920. Serial No. 413,539.

' To all whom it may concern:

Be it known that we, Bnnrmn DAwso-N COLEMAN and JOHN S. BARNER. citizens of the United States, residing at Philadelphia.

6 in the county of Philadelphia, State .of Pennsylvania, have jointly invented certain new and useful Improvements in Piston Rings; and we do hereby declare the following to be a full, clear, and. exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to piston packing rings designed to be used on the pistons of air compressors, steam engines, gas engines and in all similar machines where a snug resilient fit between piston and cylinder is essential and to the relation of such rings to their pistons.

The necessity for a snug fit between a piston and its cylinder is too well known to require much comment. A certain amount of leakage past the piston has, however, been considered inevitable and it is a fact that air compressors attaining an efliciency of seventy-five per cent. have been considered as performing excellent service. In order to minimize leakagegpast the piston, it is the universal practice toemploy a common split snap ring. This is a circular band of metal having a gap cut at one point in its circumference to permit of expansion after wear, which is seated within a groove in the cylindrical face of the piston. The fluid pressure within the cylinder working through the gap into the groove and behind the ring forces the latter outwardly and makes a tight fit between the ring and the cylinder wall. As this pressure is maintained constantly, wear on the face of the ring does not affect the fit and as the ring wears the only change is in the width of the gap. ,The natural resiliency of the ring also tends to force it outwardly against the cylinder wall and assists in maintaining a snug fit .Such a ring, al-

- though maintaining a snug fit between its outer face and the cylinder wall, is very inefiicient in preventing leakage, but its use is continued because no better ring has been designed and also because it -serves to distribute the lubrication over the face of the cylinder.

The defects of the simple snap ring are patent. Leakage through the gap is easy and inevitable and the longer the ring is used the wider becomes this the leakage through it. The use of lapped ends has been suggested as a method of preventing this leakage, but the length of the overlapping used has been insuflicient to effectively prevent the passage of fluid, and more than this, the practical difliculties encountered in machining such a ring are too great to make its use feasible. The use of a plurality of ordinary snap rings in edge contact with their gaps in staggered relation does not solve the difliculty, for the simple reason that the fluid passes through the gap in the first ring, into the space behind the rings, and thence out through the gap in the last ring. As there must always be a substantial clearance between the bottom of the groove in which the ring is seated and the inner face of the ring itself and as this clearance increases as the ring wears, it is clear that merely placing a plurality of rings edge to edge cannot solve the difliculty.

Neither can the use of concentric rings with their gaps staggered prevent this leakage. lVith such an arrangement it is, of course, impossible for the leaking fluid to pass behind the outer ring, but leakage through the gap of the outer one is unobstructed.

In order to minimize leakage behind piston rings, the width of the ring is usually made to fit accurately within its groove. The result is that carbon will collect and bind the ring tightly in its groove, after which it becomes useless.

There is another defect in the simple snap ring. As the ring wears the fluid pressure within the cylinder forces the face of the ring against the cylinder wall and widens the gap. There is thus a tendency to elongap and the greater gate one diameter of the ring, the extremities of which diameter are spaced 90 from the gap and the result is that there is greater wear upon the ring at the extremities of this diameter than elsewhere. If the ring were wholly flexible, the fluid pressure would be evenly distributed about its periphery and this tendency to elongation along one diameter would not exist. It is therefore clear that the more rigid the ring the greater the inequality of the wear and any ring approaching perfect flexibility will, in just that degree, approach acondition in which the wear is uniform.

It is accordingly an object'of this invention to devise a simple and eflicient ring which shall permit of very little leakage more outer rings in edge contact with one another encirclin the inner ring concentrically and adapted to bear against the cylinder wall. The gaps of all'these rings, including the inner one, are equally spaced about the circumference of the assemblage and are maintained in this relative position by means of retaining pins which project outwardly from the inner ring and extend into the gaps of the outer ones. The total width of the outer rings is made slightly less than that of the inner, so that there will be a slight relative movement to revent sticking, and a total width of the entire ring is made slightly less than the'groove in which it is sealed, so that there will be a movement of the ring relative to the groove with each stroke of the piston. This will prevent carbon from binding the ring tightly within the groove.

In order that the invention may be more clearly understood, reference is had to the accompanying drawings disclosing the preferred embodiment thereof, and in which Figure 1 is a vertical section through the assembled ring; Figure 2 is a plan of the ring showing the preferred relation of the gaps of the outer rings to one another and to that of the inner ring; Figures 3, 4 and 5 are side views taken in the directions of arrows 3, 4 and 5, respectively, showing the gaps of the outer rings and the relation thereto of the retaining pins, and Figure 6 is a diagrammatic section showing in exaggerated form the relations among the cylinder, piston and ring of an air compressor during normal operation.

In the drawings, 1 represents the main or inner ring provided with the usual gap 2.

Encircling this ring, and designed to make a substantially fluid-tight contact therewith, is a series of three outer rings 3, each of which is also provided with the usual gap 4. As shown most clearly in Fig. 2, the gaps of these four rings are equally spaced about the circumference of the composite ring and are retained in this relative position by means of three retaining pins 5 projecting from the outer face of the inner ring 1. One of these pins, preferably thatemployed in retaining the middle outer ring in position, is situated diametrically opposite the gap of the inner rin and the other two pins are at the extrem ties of a diameter normal to the first one. Each of these three pins is in a different plane, each plane corresponding approximately to that passing through the middle of each outer ring when all of these rings are positioned. These pins 5, as shown most clearly in Figs. 3, 4 and 5, lie within the gaps of the outer rings and serve to prevent any substantial relative circumferential displacement thereof.

The thickness of the inner ring is slightly less than that of the outer ones, the object of this being to make its flexibility comparable to that of the combined outer rings which are individually more flexible by virtue of their lesser width.

Referring to Figures 1, 3, 4 and 5, it will be 'noted that the depth or width of the inner ring is slightly greater than the combined depths of the outer rings, the purpose of which arrangement will be made clear later.

The operation of this ring as applied to an air compressor, may be easily understood by referring to Figure 6. In this figure, 6 represents the wall of the cylinder, 7, the piston, and 8 the piston groove in which the composite ring, 1-3, is seated. Let us assume that the piston is moving in the direction of the arrow and that the space above it is filled with air under pressure. This compressed air forces the ring into the position shown, tight against the wall of the cylinder, and tight against the rear side wall of the groove 8. The spaces between the piston and cylinder, and between the piston groove and the ring, are, of course, eXaggerated in this figure, but it is clear that the compressed air can readily pass through space 9 and into space 10 behind the ring. Leakage from this point on is impossible. The air may and does pass through gap of the inner ring, but it then meets the impenetrable wall of the lower outer ring 3, and as this ring is tightly pressed against the side wall of the groove, leakage here is practically impossible. The compressed air can also pass through space 9 directly through the gap in the upper outer ring, but in order to pass from this point to the gap in the second ring, it must pass between the contacting edges of the two rings and along 90. Even should this passage be made there would still remain the third ring to be passed. In other words, there is no direct passage at any point through which the compressed air may pass from one side of the piston to the other.

As the direction of movement of the piston is reversed the composite ring slides relative thereto and bears against the. opposite wall of groove 8. This movement of the entire ring prevents the formation of carbon which would tend to bind it in its groove.

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had between the outer face of the inner rings and the inner faces of the outer rings, the total depth of the latter is 'made less than that of the former. The result is that as the piston changes its direction of motion, the outer rings slide for a short distance over the face of the inner rin and thus prevent the accumulation of grit between the two rings and insure a perfect fit. It is, of course, to be understood that the lubricant works in between all of these rings and further seals them against leak age.

By spacing the gaps of the four rings 90 apart about the circumference of. the composite ring, a ring is produced having much greater flexibility than a single ring of the same depth and thickness. The greater the number of rings used in any given assembly, the greater this flexibility, but it has been found that the use of four rings results in a flexibility which is sufficient for all practiurposes. e wear of such a ring is evenlyv distributed about its circumference and the ring is thus longer lived than a simple snap ring of the same dimensions.

A ring made according to this invention is simple to manufacture as none of its parts are required to be especially machined, is

easy to use, and its parts, when worn, may

readily be replaced without necessitating the replacement of the entire ring.

Although certain specific relations among the component parts of this ring have been shown and described it is, of course, to be understood that the invention in its broadest aspects is not necessarily limited to these details. For example, although the use of four rings with their gaps s aced substantially 90 apart has been s own and described, it is clear that a greater number could be used and with a different spacing of the gaps. It'is also possible, under some circumstances, to employ only two outer rings, but on the whole the use of three or more is preferable. But such modifications, as well as others, which readily suggest themselves, are construed to fall within the scope of this invention.

We claim: I v

1. A piston ring comprising an inner ring having an outer cylindrical face and encircling outer rings, the depth of the inner ring being greater than the combined depths of the outer rings.

2. The combination of a piston having a piston groove and a piston ring seated in said groove, the .piston ring comprising an inner split ring and encircling outer split rings, t e edges of the outer split rings being in contact and the gaps in all the rings being spaced a substantial distance apart,

the width of the composite ring being less than that of the groove.

3. The combination of a piston having a piston ring groove, and a piston ring seated 1n said groove, the piston ring comprising an inner split ring and three encircling outer split rings, the edges of the outer rings being in contact, and the rings being spaced substantially 90 apart, the width of the composite ring being less than that of the groove.

4. The combination of a piston having a piston ring groove, and a piston ring seated in said groove, the piston ring comprising an inner split ring and a plurality of encircling outer split rings, the edges of the outer rings being in contact and the gaps of all the rings being spaced a substantial distance apart about the circumference of the composite ring, the inner and outer rings being mounted for slight relative movement along the longitudinal axes, and the width of the composite ring being less than that of the groove.

5. The combination of a piston having a piston ring groove, and a piston ring seated in said groove, a piston ring comprising inner and outer split rings, one of said rings comprising a plurality of split rings in edge contact, the gaps in all the rings being spaced a substantial distance apart and the width of the composite ring being less than that of the groove.

6. The combination of a piston having a piston ring groove, and a piston ring seated in said groove, a piston ring comprising inner and outer split rings, one of said rings comprising a plurality of split rings in edge contact, the gaps in all the rings being spaced a substantial distance a art and the width of the composite ring being less than that of the groove, the construction permitting a substantial movement of the ring relative to the groove with each stroke of the piston.

7. The combination of a piston having a piston groove, and a piston ring seated in said groove, the piston ring comprising concentric split rings with their gaps spaced a substantial distance apart, and the width of the composite ring being substantiall BERTRAM nAwsoN COLEMAN. JOHN s. BARNER.

gaps of all the 

